Technical Abstract:
Different recommendations exist world-wide on which, if any, pressure heads should be used in laboratory measurements to approximate the 'field capacity' (FC) of the soil. Literature often deems any such pressure heads to be inadequate to approximate FC for soils of all textures. We used a data collection from the literature to evaluate if corrections can be made to improve the estimation of FC from -33 kPa water retention (W33). Regression tree modeling coupled with jack-knife cross validation was used to identify the best predictors, sand, silt, clay, and the measured W33 value, to estimate the difference between W33 and FC. Such predictions were then successfully used to adjust the W33 value as the estimate of FC. An improvement in estimating FC was seen in general statistical terms, and texture specific bias was also greatly reduced. Such a solution may allow the reliable use of a single pressure head in the laboratory to approximate FC, which may be the only feasible option, for large scale studies.